Guam is the largest and southenmost of the Marianas Islands. It was settled from southeastern Indonedia around 2000 BCE. The Spanish explorer Ferdinand Magellan landed on Guam on 6 March 1591 during his circumnagivation of the world. Spain claimed Guam, along with the rest of the Marianas, in 1667, and colonized the island the following year. Guam was a regular stopover point for Spanish galleons traveling between the Philippines and New Spain.
During the Global War, the Mexican Navy captured the island, along with the rest of the Marianas, in 1942, after going to war with Japan and Australia, though Sobel does not say which nation controlled Guam before then. The Japanese captured the island in the latter half of 1944 during their counteroffensive against the Mexicans.
IOW, Spain surrendered Guam to the United States of America in 1898, while the rest of the Marianas became a German possession, then were taken by the Japanese in 1914. The Japanese occupied Guam from December 1941 to July 1944, when the island was recaptured by the U.S.A. Due to its history, Guam is administered separately from the rest of the Marianas Islands.